Time or phase delays in electrical signals are often used in various applications, such as, for example, electrically controlled antennas, phase shifters and frequency tuning of resonators in filters and oscillators.
For use in oscillator circuits, various principles using delay lines have been disclosed. A problem with delay lines in oscillators is that the delay provided by the delay lines must be very precise, due to the fact that the delay is optimal for a single frequency only, which thus makes the circuit sensitive, and necessitates a high degree of precision in the design and manufacture of the delay lines. In addition, the circuit becomes very sensitive to component variations in, for example, temperature and ageing.
Also, in circuits of the kind described, frequency tuning with maintained performance tend to be difficult, and the sensitivity for parameter variations tends to increase with increased performance of the oscillator circuit.